The first app to be written right now is Geoquiz, who can test the user's geographic knowledge. The user answers the question on the screen by clicking the True or False button, Geoquiz can instantly feedback the answer correctly or not.
Figure 1-1 shows the result of the user clicking the false button.
1.1 Application Basics
The Geoquiz application consists of an activity and a layout.
activity is a specific instance of the activity class in the Android SDK that manages the user's interaction with the information screen. The function of the application is implemented by writing activity subclasses. A simple application might require only one subclass, and a complex application would have multiple sub-classes.
A layout defines a series of user-interface objects and where they appear on the screen. The definition of the composition layout is saved in the XML file. Each definition is used to create a pair of lines on the screen, such as a button or text message.
(original) "Android Programming Authority Guide" learning note 01--Android app first experience--001